The present invention relates to a rock drilling device for drilling in rock by means of a drill string comprising a set of tubes, and a set of rods arranged in the set of tubes and comprising a number of rods abutting loosely against each other.
When drilling with drill strings of the above mentioned kind it is essential that the rods forming the set of rods abut against each other when the hammer piston impacts the rearmost part of the set of rods so that the energy of the hammer piston is transferred to the drill bit at the other end of the drill string without unnecessary losses. This problem has been solved by means of the device according to U.S. Pat. No. 4,993,504. In the thus known device one still has problems when the drill bit penetrates into weaker formations. It has turned out that the set of rods in certain situations can sink down so that the projections, which are provided in order to prevent the rods from falling out from the set of tubes, come in contact with the tubes so that these are damaged by the impacts which the rods are exerted to by the hammer piston. It has also turned out that the pressure decrease which is obtained in the recoil damper can result in damages on the machine housing caused by the recoil from the set of rods.